For example, JP-2011-131696-A discloses an input rod for a vacuum brake booster, and JP-2006-282001-A discloses an input rod for a hydraulic brake booster.
In obtaining an input rod for a brake booster, for example, a round rod is forged to produce a semi-finished input rod product having a main shaft portion of an input rod. Thereafter, a boot installing groove is formed on an outer circumference of a middle portion of the semi-finished input rod product through cutting, and an external thread on which a yoke is screwed is formed at a rear end portion of the semi-finished input rod product through rolling. In these working steps, particularly, the boot installing groove cutting takes a relatively long time. Additionally, cuttings need to be disposed of, and this tends to increase the production costs, making it difficult to reduce the product price.